I’d love to have seen Pink Floyd. And Kylie, but not in concert 
For me, the best one was either The Ramones in Brixton, or as a sheer spectacle, The Pet Shop Boys at Wembley. For nostalgia purposes, then I went to every OMD and Depeche Mode tour in the 80s when they played the small and intimate Hammersmith Odeon and they were always sweaty affairs Worst one ever was Prince at Wembley…about as exciting as watching paint dry LOL.